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Honing the science of finding survivors

The Coast Guard is constantly refining its crucial drift calculations for better search precision

Worst-case scenario: The boat has sunk, its crew are in the water and the Coast Guard isn’t sure where they are. That’s when the Search and Rescue Optimal Planning System, or SAROPS, starts earning its keep.

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“We are very, very good at assisting and rescuing people,” says Arthur Allen, a Coast Guard Office of Search and Rescue oceanographer who helped create SAROPS. “If you tell us where you are, chances are very good we can recover you. But if you can’t tell us where you are, we’ve got more of a problem.”

SAROPS, activated in January 2006 at 51 Coast Guard operations centers, calculates the drift of a disabled boat, life raft or survivor in the water. It projects where wind and currents have carried — and where they are likely to carry — the survivors. It also helps rescuers work out the best search plan with the vessels and aircraft at their disposal, even if they have only the vaguest idea of where a boat was when it got into trouble.

Needle in a haystack

Straightforward as that sounds, it is not.

Allen has spent the better part of a 25-year Coast Guard career figuring out how different objects — boats, life rafts, sea kayaks, people, people wearing PFDs, people not wearing PFDs, people wearing immersions suits, fat people, skinny people — drift in the water under all kinds of conditions. “That was a good chunk of what I did for 20 years,” he says. His findings are incorporated into SAROPS.

Now Allen and his colleague, Chris Turner, at the Coast Guard Research and Development Center in Groton, Conn., are tweaking SAROPS to make it work even better.

The accuracy of drift projections depends a lot on what rescuers know initially about the survivors’ last known location, whether they are on the boat or in the water, if they are on a life raft or wearing a PFD, and also the quality of information about winds and currents. Allen says getting winds and currents for offshore waters isn’t that hard, but finding good sources of information about inshore waters — small bays, estuaries and harbors — is a challenge. “The topography is more complex, the problems are more complex,” he says.

He is always looking for more and better sources of wind and current information while Turner, another oceanographer, has been working with University of Portsmouth (England) physiology Prof. Mike Tipton and mathematicians at the U.S. Army Natick (Mass.) Soldier Systems Center to refine the ability of rescuers to project how long the people they are searching for can survive in the water. Better survival projections better equip rescuers to make some very difficult decisions.

“It is a very highly charged situation when someone goes missing,” says Turner.

He is trying to ratchet up the level of certainty a search controller has that he is searching for survivors, not bodies. Often search controllers must decide when it is no longer realistic to search, because by even the most conservative estimate the people they are looking for are almost certainly dead. Or, they may have to decide when it is time to shift resources from looking for victims who likely are dead to focusing on those who still may be alive.

“That is clearly a difficult decision to make,” says Allen. “When do you suspend active searching? That is not done lightly. It’s only done when they have taken into account all possible factors and given survivors every benefit of the doubt.”

Assessing survivability

Tipton, co-author with Frank Golden of “The Essentials of Sea Survival” (Human Kinetics, Champagne, 2002), the authoritative text on cold-water survival, says rescuers may be looking for some people with PFDs on, some with no PFDs, some with immersion suits, others on life rafts — all at the same time. The survival time and drift rates for all these people are different.

The crew of an Alaskan fishing vessel await rescue in a life raft adrift in the Bering Sea.

“You’re trying to optimize your search to maximize your chances of finding people [alive] who may be in very different situations in the water,” Tipton says. “It’s pointless to keep searching for guys in their pajamas when it’s way beyond the time they could have survived, and time to move on to searching for the guys in immersion suits and life jackets.”

Tapping into 20 years of data that the U.K.’s Institute of Naval Medicine and Royal National Lifeboats Institution gathered from sea rescues, Tipton has compiled a database of how long people survived in the water and correlated it with sea state, water temperature, age of survivors, the clothes they wore, their gender, fitness, body type, whether they wore a PFD or immersion suit, and other factors.

Derived from 1,600 cases in the institute’s archives — mainly cold-water cases, plus some 500 warm-water cases provided by the Coast Guard — Tipton’s data is able to tell a search controller that “no one [in the database] has survived beyond 14 hours at this water temperature and in this sea state,” he says.

In addition to water temperature, Tipton says his analysis of the data suggests that the most important factors in how long people last in the water are sea state, whether they are in coastal or offshore waters, their age, how much clothing they are wearing and whether they are wearing a PFD.  “The statistics show that you are eight times more likely to survive if you’re wearing a PFD than if you’re not,” he says.

The Coast Guard already has a computer program that is quite effective in projecting when hypothermia is likely to set in, “but [Tipton’s work] will significantly upgrade our survival modeling,” Allen says. The new program could be operational in 2009. It not only can help the Coast Guard use its assets more efficiently, but make for better rescue operations.

“If you’re in the water, you want them looking for you until there is no hope [that you’re alive],” Allen says. “If you’re in the life raft, you don’t want the Coast Guard to be out there looking for dead bodies. You want them looking for your life raft.”

This article originally appeared in the March 2009 issue.